1. Field of the Invention
The present invention relates to an image processing method and apparatus suitably used for obtaining a distance image from a series of tomogram images when a three-dimensional binary image of an object is viewed from an arbitrary direction, obtaining a normal image from the obtained distance image, and obtaining a shading image of the object from the obtained normal image.
2. Description of the Related Art
Recently, it has been attempted to form a three-dimensional binary image of an object from a series of two-dimensional tomogram images obtained by a CT scanner or the like. In order to stereoscopically display the shape of a three-dimensional binary image of an object when viewed from an arbitrary direction by shading, a distance image from an observing point must be obtained. A distance image is obtained as density data which represents distances from the respective points of a desired plane including an observing point, i.e., points corresponding to the respective pixels in an area corresponding to one screen defined within the plane, to the surfaces of corresponding portions of an object represented by a three-dimensional binary image. However, since the data size of a three-dimensional image becomes large and hence large-scale processing is required as compared with a two-dimensional image, a long period of time is required to obtain a single distance image.
According to another method, a normal image is obtained from a distance image, and a so-called shading image is obtained by calculating the luminance of a surface of an object when a light beam is radiated onto the object from an arbitrary direction on the basis of the obtained normal image. However, the amount of luminance calculation required by this method enormous, and hence a long period of time is required to obtain a single shading image.